The invention relates to a small size tape recorder with adapter, and more particularly, to such apparatus with an adapter which may comprise a variable speech control circuit for compressing or expanding the time axis of the recorded content or a microcomputer circuit.
The provision of additional functions in a small size tape recorder by coupling an adapter therewith has been already in practical use with a miniature-size tape recorder developed by the present applicant which employs a micro-cassette. In this instance, the inherent function of a tape recorder is minimized so that the entire assembly can be received in a pocket while allowing an operative coupling with an adapter to provide additional functions.
As is well known, the tape feed rate in a tape recorder is normally variable only within an extent from about +3% to -20% of a standard feed rate. If the feed rate changes as much as +50% or -25%, there occurs a considerable variation in the tone quality to present difficulties in hearing. A further variation as much as +100% or -50% will make the hearing impossible entirely. Hence, it is seen that it is impossible to improve the hearing efficiency by reducing the length of time which is required for the playback, by using a tape feed rate which is increased as much as +100%. On the other hand, it is also impossible to reduce the tape feed rate as much as -50% for purpose of stenographer's use.
Recently, a so-called variable speech control technique has been developed which compresses or expands the time axis of the recorded content by utilizing the redundancy of the speech, through a change of the tape feed rate and an adjustment of frequencies during the playback. Means which takes avail of the variable speech control includes a tape speed control knob which provides a control voltage which is applied to a motor control circuit to change the number of revolutions of a tape drive motor, thus changing the running speed of a magnetic tape. In addition, the control voltage is also applied to a pitch conversion circuit and also to a variable playback equalizer which compensates for a variation in the response of signals being reproduced which may be caused by a change in the tape speed. In this manner, the tape speed can be arbitrarily and continuously changed within a range from one-half to two and one-half times the standard rate.
When a tape speed which is twice as high as the standard rate is established, the signal reproduced by a playback head will have a doubled frequency while the playback time will be reduced to one-half. The reproduced signal is then passed through a preamplifier and the variable playback equalizer before it is applied to the pitch conversion circuit which processes the signal with a pitch conversion factor of 1/2 to restore the original pitch. The signal supplied from the pitch conversion circuit will be one-half times the original length of the recorded content which will be obtained when the tape runs at its standard rate. The restored content comprises a succession of segments which are obtained by splitting the original content into adjacent lengths and picking up one-half of each of them. In this manner, the redundancy of speech and non-recorded length of the tape can be cut off while assuring a satisfactory recognition of the content of the speech.
It is also known to use a programmed microcomputer circuit for automatic operation of the tape recorder. However, it is recognized that the variable speech control circuit or microcomputer circuit is formed by a plurality of IC or LSI components which require a high voltage source. These IC or LSI components which are commercially available are of a large size, having electrodes which are disposed at 0.1 inch pitch. This makes it difficult to assemble the variable speech control circuit into a small size tape recorder such as miniature tape recorder developed by the present applicant. The use of commercially available IC or LSI components is almost prohibitive since they require a high voltage and high capacity power supply.
It then may be contemplated to provide these circuits in the form of an adapter incorporating commercially available IC or LSI components. The adapter then must internally house a high voltage and low capacity power supply such as layer-built cells capable of supplying 6, 9 or 12 volts, as contrasted to a low voltage and high capacity power supply of the recorder which may comprise a pair of dry cells supplying 3 volts. A high voltage supply of a small size such as silver, alkali-manganese battery is available which can be used to operate both the tape recorder and IC or LSI components. However, the output amplifier and the motor contained within the tape recorder represent high power dissipation components, which cause such an expensive power supply to be rapidly exhausted, thus resulting in an increase in the cost. In addition, the battery must be frequently replaced. Where a separate power supply is provided to operate the adapter, there is a possibility that its power switch may be left closed when the adapter is not used, causing a wasteful dissipation of the power supply.